The invention relates in general to submunitions and grenades and, more particularly, to an environmentally-energized safety, arming, and detonation device for a submunition, which is more reliable and safer than conventional devices.
Known dual-purpose improved conventional munition (DPICM) grenade fuzes such as the M223 and M234 detonate the grenade warhead on impact with ground or target through use of an inertial stab bolt or firing pin and a stab detonator. The grenades are stacked in a mechanically safe (unarmed) state inside a rocket or “cargo” round. When grenades are stacked in the cargo round, the tip end of the threaded firing pin engages the arming slider and prevents the arming slider from moving into the armed position. Since the slider must be moved for the explosive to detonate, the grenade cannot be detonated, and, as stored, is safe.
When expelled from its carrier round (such as a missile or projectile), the grenade is moving at the carrier's forward velocity and may tumble in the airstream. The grenade is quickly oriented, stabilized and decelerated by a ribbon loop that is extended from the top of the grenade fuze. Depending upon the carrier, e.g., artillery or rocket, the grenade may have a relatively high or low spin rate, respectively. An end of the stabilizer ribbon is attached to a threaded firing pin inside the grenade.
As the grenade falls, the drag or spin of the ribbon produces a relative rotational force between the grenade and ribbon. That rotational force with drag tension turns the threaded firing pin out of a threaded collar and extracts the stab bolt tip from a retaining hole or socket in a slider, disengaging the tip of the firing pin from the arming slider. The arming slider contains a stab-initiated detonator that can be in an aligned or non-aligned state with reference to the stab bolt and the grenade warhead. Released from the hold of the pin, the slider is forced radially outward, by a combination of the centrifugal force of the rotating grenade and/or an arming spring to a radial position at which the stab detonator carried in the grenade becomes aligned with both the lead explosive charge and the line of action of the firing pin. At that point in the flight, the grenade has become fully armed, and the arming spring holds the slider in that fully armed position.
On grenade impact, the stab firing pin, which has been de-threaded from the threaded collar, is free to move under inertial (e.g., impact) forces such that it initiates the stab detonator, which initiates the explosive train through contact with the lead charge at a high velocity. As is typical of this type of DPICM fuze, however, the required striking action by the firing pin is not very reliable because its mechanical sensitivity depends on the angle of impact. Impact by the submunition must be very close to vertical with respect to the grenade axis and with sufficient force and abruptness for the firing pin to operate properly. Additionally, the ribbon that is deployed to unscrew the firing pin is unreliable. For slow spinning or nonspinning rounds, such as those carried by rockets, the ribbon does not generate enough spin on its own to reliably unscrew and release the firing pin.
Current DPICM fuzes generally have low primary reliability (function on target), as low as 96% or less, which means that the population of grenades deployed by the weapon automatically loses, in the aggregate, up to 4% of its effectiveness on first impact with the target. One of the primary causes of this unreliability is the poor off-axis sensitivity of the current stab-detonator mechanisms. One response to this reliability problem by grenade manufacturers is to use some type of self-destruct (SD) mechanism in the fuze.
An electromechanical version of a self-destruct mechanism includes a battery ampoule, an electronic timer, and a capacitor. When the slider is forced radially outward, a spiral locking mechanism releases a battery activator, which ruptures an ampoule of a reserve battery. During the movement of the battery activator, an electrical short-circuit is also removed so that as the battery charges, it activates the electronic timer. If the grenade fails to function upon impact and after a lapse of a predetermined time, the capacitor discharges into the electro-explosive device next to the detonator, which causes the munition to function. In a pyrotechnic delay version of a self destruct mechanism, the pyrotechnic delay mix initiates immediately when the slider moves into the armed position, and if the grenade fails to function upon impact after a lapse of a predetermined time, the pyrotechnic delay train initiates the detonator.
However, the addition of a time-delay self-destruct (SD) mechanism, whether pyrotechnic or electronic in function, introduces new hazards. For example, a DPICM-loaded Multiple Launch Rocket System (MLRS) rocket battery or an MLRS-bearing mobile platform may suffer damage leading to unintended grenade dispense. This damage can occur due to a rocket-propelled grenade (RPG) attack or the impact of an improvised explosive device (IED) or an incident in a munitions depot. Some of the released grenades can tumble or roll and release the arming slider, which (in known designs) automatically initiates the self-destruct mechanism. An even greater hazard results from accidental dispense of the described self-destruct type grenades due to damage to a mobile platform carrying MLRS type rockets, for example, on the deck or in the hold of a ship or in an air vehicle while it is being carried. Also, the SD mechanisms also are not highly reliable.
Duds on the battlefield in which both the impact destruct and SD functions have failed are highly dangerous because they remain mechanically armed after dudding and can be detonated at any time by handling or jostling that moves the inertial detonator pin. Additionally, the SD mechanisms add undesired complexity and cost to the current DPICM fuze. One part of that complexity is that electrically enabled SD mechanisms require batteries, which add considerable expense and have limited reliability.
The prior art fuze occupies a significant portion of the package of the grenade and relies solely upon a series of mechanical operations to arm and ready the grenade for detonation upon impact with a target. Should the impact function fail, the result is an armed unexploded grenade, a “hazardous dud”. The inclusion of the self-destruct mechanism does little for primary reliability (function on target) but does detonate and therefore clean up a proportion of the hazardous duds. Due to the large quantity of grenades typically deployed in the various munition delivery vehicles (e.g., MLRS rockets), however, there may remain a significant quantity of hazardous duds that can be triggered upon contact by vehicle or personnel walking though the battlefield
Additionally, in the known fuze, there is stored energy (a compressed spring) that tends to move the arming slider into the armed position once the grenades are de-nested. In an accident or warfare scenario wherein an unlaunched missile containing submunition grenades is ruptured or blasted apart, there will be some twisting and rolling of grenades relative to their stabilizer ribbons. This twisting or rolling may be sufficient to unscrew the stab pin or bolt from its captive state, which releases the arming slider. In an accident scenario numerous armed duds may be produced, resulting in a very hazardous situation.